A watching eye over the planning permissions being granted in London confirms a trend that’s been obvious for some time. The basement bug has bitten those Londoners who are living in ground floor flats, in ordinary areas (if such a thing as an ordinary area exists in London). In fact, this is part of a general movement among architects and London residents to make the most of small houses and flats.

Basement companies in London are used to dealing with the idiosyncrasies of local planning regulations when it comes to basement excavations and extensions. The companies with years of experience actually know how the various London boroughs are likely to react to different kinds of plans and designs. That’s part of what you pay for when you hire a company with experience: they can probably tell you in advance what is and isn’t going to fly with the local borough planners. This can save you a lot of money in wasted plans and applications.

Local boroughs have local concerns when it comes to basements

Some companies doing basement conversion in London find it surprising and frustrating that every borough varies in what it will accept. But really, it’s a strength – because each borough has a different environment and set of priorities for local people. Take flood risk – it’s inevitably influenced by how near a borough is to the River Thames and the properties of the water table in the borough.

Similarly, while some boroughs have a lot of property with basements, where it’s more a case of an extension, others have many houses with cellars, or no basement, where an excavation will be needed. If the property is on a main route into London, traffic flow and other considerations will come into play. So it’s not simple.

The Basement Impact Assessment

Many councils use a Basement Impact Assessment as part of the planning process. This is a document that assesses the effect of the basement on both the natural environment and the surrounding buildings. The Royal Borough of Kensington and Chelsea was the first council to introduce them because, in the early days, London basement excavations were very much the preserve of the wealthy in prime central London.

However, since then other councils have taken to them with some enthusiasm. One of the problems reported by architects and others is that the council approach isn’t scalable. So a major project that would alter a street, stop traffic and cause a lot of disruption has the same level of paperwork as a minor basement extension to a small house.

If you don’t know the difference between a hydrologist and a hydrogeologist, or why you may need both, one or neither, be careful about signing up for a basement project. You need a firm that’s technically capable but also has some values and ethics and is committed to quality assurance. Look for membership of BSWA, the body that ensures people know what they’re doing with waterproofing, and other schemes such as Considerate Constructors, which tend to be a marker of more responsible firms.